Add news section for PETSc < 3.5 end of support (idaholab#19197)

modules/doc/content/newsletter/2021_10.md

@@ -6,6 +6,11 @@ The effort to extract the python tools from MOOSE into a more generic set of too
 has been halted. If the need for this effort changes it may be considered again
 in the future.
 
+## Support Ended for PETSc < 3.5
+
+Support was [ended this month for PETSc versions older than 3.5](https://github.com/idaholab/moose/pull/19197),
+and MOOSE code references corresponding to these prior versions have been removed from the framework.
+
 ## MOOSE Improvements and New Features
 
 ### Reactor Module